Inorganic polysilazane resin

ABSTRACT

An inorganic polysilazane resin of the present invention has a Si/N ratio (i.e. a ratio of contained silicon atoms to contained nitrogen atoms) of 1.30 or more. The inorganic polysilazane resin having such a high Si content can be produced by, for example, a method in which an inorganic polysilazane compound containing both Si—NH and Si—Cl is heated to react NH with Cl, a method in which a silazane oligomer (polymer) that leaves no Si—Cl bond is synthesized and a dihalosilane is added to the synthesized silazane oligomer (polymer) to perform a thermal reaction, and the like. A siliceous film can be formed by, for example, applying a coating composition containing the inorganic polysilazane resin onto a base plate and then dried and the dried product is then oxidized by bringing the dried product into contact with water vapor or hydrogen peroxide vapor and water vapor under heated conditions.

FIELD OF THE INVENTION

The present invention relates to an inorganic polysilazane resin, morespecifically, to an inorganic polysilazane resin which can be suitablyused for forming an insulation film, a passivation film, a planarizationfilm, a protective film, a hard mask, a stress adjusting film, asacrifice film, and the like of electronic devices such as asemiconductor element, etc. The present invention also relates to acoating composition containing the inorganic polysilazane resin, amethod for forming a siliceous film by use of the inorganic polysilazaneresin, and a siliceous film formed by the method.

BACKGROUND ART

A polysilazane is well known as a compound useful for a precursor ofsilicon nitride (for example, see Patent literature 1 below). In recentyears, it has also attracted attention as a material for forming aninsulation film such as an interlayer insulation film, a passivationfilm, a protective film, a planarization film, and the like of theelectronic device such as a semiconductor device. These films are formedby applying a coating liquid containing a polysilazane to an appropriatesubstrate, followed by baking to transform the polysilazane to asiliceous film (for example, see Patent literatures 2 to 5 below).

In addition, in the electronic device such as a semiconductor device, asemiconductor element such as a transistor, a resistor, etc. arearranged on a substrate and for electrically isolating and separatingthese elements, an isolation region which is composed of an insulationfilm is formed between the elements by using a polysilazane,Furthermore, in the field of the electronic devices, densification andhigh integration of the elements have been proceeded and in order tocope with these densification and high integration, a trench isolationstructure, which is produced by forming a fine groove on a surface of asemiconductor substrate and filling the groove with an insulatingmaterial to electrically separate between elements formed at both sidesof the groove, has been adopted.

A coating liquid containing a polysilazane is used also in theaforementioned trench isolation structure. As a polysilazane used forforming insulation films including the trench isolation structure,passivation films, planarization films, protective films etc., there isexemplified, in Patent document 1, an inorganic polysilazane having arepeating unit represented by the following formula;

As a synthesis method of a polysilazane, Patent document 1 discloses amethod in which adducts of dihalosilane with a base are reacted withammonia. In addition to this, various other methods have been proposedfor synthesizing a polysilazane, for example, (a) a method of reacting asilicon halide such as SiCl₄, SiH₂Cl₂ or the like with an amine, (b) amethod of producing a polysilazane from a silazane by use of adehydrogenating catalyst consisting of an alkali metal hydride such asKH, (c) a method of synthesizing a silazane by a dehydrogenationreaction of a silane compound with an amine compound by use of atransition metal complex catalyst, (d) a method of performing an amineexchange of aminosilane with ammonia by use of an acid catalyst such asCF₄SO₃H, (e) a method of performing an amine exchange of an aminosilanewith a large amount of ammonia or amine, (f) a method of performing anamine exchange reaction of a polyvalent aminosilane with apolyhydrogenated nitrogen-containing compound in the presence of a basiccatalyst, etc. (for example, see Patent document 6).

By the way, various properties such as an insulation property, aflatness of a film, a resistance for an acid, an alkali, a solvent, andthe like, a high barrier property, and so on are required for theinsulation film, the passivation film, the protective film, theplanarization film, and the like in the electronic device such as thesemiconductor device. Though a film fulfilling these properties can beproduced by the aforementioned method for forming a siliceous film witha coating liquid containing a polysilazane, shrinkage of the film and ageneration of a residual stress arise upon baking a polysilazane toconvert into a siliceous film. When the shrinkage or residual stress ofthe film is large, there occur problems like that cracks and a crystaldefect of the substrate. For this reason, a polysilazane which shrinkageand residual stress are suppressed as much as possible, are expected. Inaddition, it is desirable to form a high density siliceous film in orderto obtain good etching properties in the trench isolation structure.

CITATION LIST

-   Patent document 1: JP 63-016325 B-   Patent document 2: JP 2011-054898 A-   Patent document 3: JP 2005-045230 A-   Patent document 4: JP 09-031333 A-   Patent document 5: JP 09-0275135 A-   Patent document 6: WO 97/24391 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention was made under the situation above and an objectof the present invention is to provide an inorganic polysilazane resinwhich can form a siliceous film having the same properties as those ofthe conventional siliceous film, i.e. a good insulation property, a goodfilm planarity property, a high resistance to an acid, an alkaline and asolvent etc. and a high barrier property, as well as form a siliceousfilm with a small shrinkage and a small residual stress. Another objectof the present invention is to provide a coating composition containingthe inorganic polysilazane resin, a method for forming a siliceous filmby using the inorganic polysilazene resin, and a siliceous film formedby the method for forming a siliceous film.

Means for Solving the Problems

As a result of intensive studies and investigations, the presentinventors found that a ratio of silicon atoms and nitrogen atoms, whichconstitute the inorganic polysilazane resin, is important and when theratio, Si/N is made 1.30 or more, a high density siliceous film wasobtained and various properties of the siliceous film remain as it is,i.e. a good insulation property, a good film planarity, a highresistance to an acid, an alkaline and a solvent etc., and a highbarrier property, and the problems of a shrinkage and residual stress ofwhich are improved. The present invention was accomplished based onthese findings.

The present invention, therefore, relates to an inorganic polysilazaneresin, a coating composition containing the inorganic polysilazaneresin, a method for forming a siliceous film by using the inorganicpolysilazene resin, and a siliceous film formed by the method, asmentioned below.

(1) An inorganic polysilazane resin, wherein a ratio of containingsilicon atoms to containing nitrogen atoms, Si/N is 1.30 or more,preferably 1.32 or more.

(2) The inorganic polysilazane resin described in (1) above, whichweight-average molecular weight is 1,200 to 20,000 in terms ofpolystyrene.

(3) The inorganic polysilazane resin described in (1) or (2) above,which is produced by heating an inorganic polysilazane compoundcontaining both Si—NH and Si—Cl to react NH with Cl.

(4) The inorganic polysilazane resin described in (3) above, wherein theheating is conducted in the presence of a catalyst.

(5) The inorganic polysilazane resin described in (4) above, wherein thecatalyst is a tertiary amine.

(6) The inorganic polysilazane resin described in (1) or (2) above,which is produced by synthesizing a silazane oligomer or polymer with noSi—Cl bond and then adding a halosilane, for example, a dihalosilane tothermally react these compounds.

(7) A coating composition containing the inorganic polysilazane resindescribed in any one of (1) to (6) above.

(8) A method for forming a siliceous film, wherein the coatingcomposition described in (7) above is applied to a substrate andoxidized by contacting with a water vapor under a heated condition afterdrying.

(9) A method for forming a siliceous film, wherein the coatingcomposition described in (7) above is applied to a substrate andoxidized by contacting with a hydrogen peroxide vapor and a water vaporunder a heated condition after drying.

(10) A siliceous film, which is formed by the method for forming asiliceous film described in (8) or (9) above.

(11) The siliceous film described in (10) above, a shrinkage of which is15% or less.

Advantageous Effect of the Invention

As the inorganic polysilazane resin of the present invention has a highcontent of silicon, a siliceous film formed by using this resin can forma higher density siliceous film in comparison with a film formed byusing a conventional polysilazane resin. By this reason, a siliceousfilm having a smaller shrinkage and a smaller residual stress than thoseof conventional siliceous films can be produced. Therefore, theinorganic polysilazane resin of the present invention is effective oneliminating cracks in the film and crystal defect of the substratebecause the shrinkage and residual stress of the film are small, whenusing to form an insulation film, a passivation film, a protective film,a planarization film, and the like of the elements used in the field ofelectronic devices.

Mode for Carrying Out the Invention

The inorganic polysilazane resin of the present invention is aninorganic polysilazane resin in which the ratio of containing siliconatoms to containing nitrogen atoms (Si/N) is made to 1.30 or more asdescribed above. The ratio of containing silicon atoms to containingnitrogen atoms (Si/N) is preferably 1.32 or more, more preferably 1.40or more. One solution for obtaining such inorganic polysilazane resinhaving a high silicon atom ratio such as 1.30 or more is to introduce atrifunctional nitrogen atom into the resin, wherein all of atomic bondsof a nitrogen atom are connected to silicon atoms as mentioned below.

For example, an inorganic polysilazane resin produced by ammonolysis ofdichlorosilane according to the method described in Patent literature 1has usually a repeating unit represented by the following formula (I)mainly. Namely, it contains essentially a bifunctional nitrogen. Theratio of silicon atoms to nitrogen atoms (Si/N) of the polysilazaneresin consisting of the following repeating unit is 1.0.

However, as a disproportionation reaction of hydrogen occurs at thesynthesis actually, it is assumed that SiH and SiH₃ exist in the resin.When SiH is formed, it is assumed that the repeating unit represented bythe following formula (H) is formed. The ratio of silicon atoms tonitrogen atoms (Si/N) of this repeating unit becomes 0.67.

In contrast, a polymer containing a trifunctional nitrogen atom isrepresented by the following formula (III). In this case, the ratio ofsilicon atoms to nitrogen atoms (Si/N) of this repeating unit becomes1.5.

*(SiH₂)_(1.5)—N_(n)*  (II)

If SiH₃ exists at the terminal as shown in the following formula (X),the ratio of silicon atoms to nitrogen atoms (Si/N) does not fall below2.0 though the value of the ratio may be changed by the molecularweight.

From these aspects, the polysilazane resin having a trifunctionalnitrogen atom has a higher content by percentage of silicon atom in therepeating unit than that of the polysilazane resin having a bifunctionalnitrogen atom. Accordingly, when the trench insulation film having atrench isolation structure is formed by using a polysilazane containingthe trifunctional nitrogen atom, a film having a higher density will beable to be produced due to a larger amount of silicon will be introducedinto the trench as compared with a case an insulation film is formed byusing a polysilazane resin containing mainly a bifunctional nitrogenatom.

The inorganic polysilazane resin of the present invention, wherein theratio of silicon atoms to nitrogen atoms is 1.30 or more, may beproduced by an arbitrary method. As an example thereof, the number ofthe nitrogen atom having a trifunction linkage should be increased inthe production of a polysilazane resin. For example, a method comprisingthe steps of;

(a) ammonolysis of dichlorosilane in an organic solvent to form anoligomer containing both chlorosilane and a NH group,(b) then, heating the system to polymerize the oligomer obtained in thestep (a), and(c) terminal treatment of Si—Cl remained in the resin with ammonia, ifnecessary.

In the aforementioned example, a method using a dihalosilane as ahalosilane is mentioned but the halosilane may be a trihalosilane or atetrahalosilane. In addition, a catalyst may be added in the process ofthe step (b), if needed. A preferred compound as the catalyst is atertiary amine.

As the step (a) which is a step producing the oligomer, arbitrarymethods including conventionally known·methods can be adopted. As anexample thereof; there is a method for synthesizing aperhydropolysilazane (PIPS) at the same condition as that of a usualperhydropolysilazane except for adjusting the amount of ammoniaintroduced. The amount of ammonia introduced is suitably ⅔ mol relativeto 1 mol of halosilane such as dichlorosilane, but is not limited tothis. When ammonia is used in this ratio, an oligomer having a lowdegree of crosslinking and a high solubility in a solvent is given. If alarger amount of ammonia is used, N—H bonds will remain. On the otherhand, if a smaller amount of ammonia is used, excess Si—Cl bonds remain.When the molar ratio of ammonia to dichlorosilane is made 2:3, thefollowing oligomer is obtained.

In this way, a polysilazane compound containing both Si—NH and Si—Cl ina molecular is formed. When the compound is heated to react NH with Cl,a polysilazane resin in which a ratio of silicon atoms to nitrogenatoms, Si/N is 1.30 or more, preferably 1.32 or more can be easilyproduced as shown below. The heat-polymerization step will be describedin detail in the explanation of the step (b).

Furthermore, a polysilazane resin in which a ratio of silicon atoms tonitrogen atoms, Si/N is 1.30 or more, preferably 1.32 or more can bealso produced by synthesizing a polymer with no Si—Cl bond, adding ahalosilane such as dichlorosilane to this, and then heat-reacting these.The method comprising the steps of;

(a) ammonolysis of dichlorosilane in an organic solvent to produce apolymer containing virtually no chlorosilane,(b) then, adding a chlorosilane-containing material to the system andheating the system to polymerize the chlorosilane-containing materialwith the polymer obtained in the step (a) (see the following formulae,for example), and(c) terminal treatment of Si—Cl remained in the resin with ammonia, ifneeded.

In addition, in the step (b), a catalyst may be added, if necessary. Apreferred compound as the catalyst is a tertiary amine.

As an example of the ammonolysis described above, a method of reacting adihalosilane represented by the formula: SiH₂X₂ (wherein, X representsF, Cl, Br or I) with a base to form adducts of dihalosilane and thenreacting the adducts with ammonia (see Patent literature 1, for example)will be explained hereinafter. As the dihalosilane used in the reaction,dichlorosilane is particularly preferred from the point of view ofreactivity and price of a raw material. The halosilane is acidicgenerally and can be reacted with a base to form adducts. Theadducts-forming rate and the stability of adducts depend on the degreeof an acidity of halosilane and the basicity degree and steric factor ofthe basic material. Therefore, by selecting the kinds of the halosilaneand the base suitably, there can be produced stable adducts by which aninorganic polysilazane resin can be easily produced. This stability ofadducts does not necessarily mean a stability of such a degree that canbe isolated as adducts. It includes all the cases such as a case thatadducts exist stably in a solvent and a case that adducts functionsubstantially as a reaction intermediate.

Examples of the base include a Lewis base, tertiary amines, pyridine,picoline and derivatives thereof, secondary amines having a sterichindrance group, phosphine, stibine, and derivatives thereof. Of these,bases having a low boiling point and a smaller basicity than ammonia arepreferred and pyridine and picoline are particularly preferred from thepoint of view of handling and economic efficiency. Furthermore, the baseshould be used in a stoichiometric excessive amount to the silane. Theammonolysis is conducted in a reaction solvent, for example, a lightsolvent such as hexane, benzene, pyridine, methylene chloride, ether,and acetonitrile. As pyridine used as a base can be also used as asolvent, it is preferred that the oligomer is formed by adding adihalosilane to excessive pyridine, followed by injecting ammonia intothe solution to ammonolysis, from the point of view of simplicity ofreaction processes and the like. This reaction is proceeded by, forexample, the following processes. That is, dichlorosilane having apurity of 99% or more is injected into dehydrated pyridine adjusted tothe temperature of −40° C. to 20° C. under stirring, and incontinuation, ammonia having a purity of 99% or more is injected intothe solution adjusted to the temperature of −40° C. to 20° C. understirring. The amount of ammonia is suitably made to an amount of ⅔ molesrelative to 1 mole of dihalosilane as described above. In this step, acrude polysilazane and ammonium chloride which is a by-product areproduced. The ammonium chloride produced by the reaction can be removedby a filtration, if needed.

Next, the step (b) will be explained. The step (b) is a step in which a(condensation) polymerization of the oligomer produced in the step (a)is carried out by heating. In the step (b), the oligomer is heated inthe dissolved state in a reaction solvent. For example, when theoligomer was produced by adding a dihalosilane to an excessive amount ofpyridine followed by adding ammonia to the reaction liquid obtained asdescribed above, an organic solvent is optionally added to the reactionliquid obtained in the step (a) and then the reaction liquid is heatedto remove ammonia. At this time, the reaction temperature, reaction timeetc. are regulated as a polysilazane having a polystyrene conversionweight-average molecular weight of 1,200 to 20,000 can be obtained. Theregulation of the molecular weight may be conducted by other methodssuch as regulating the concentration of the reaction system, thereaction pressure, and the stirring speed.

In the step (b), a trifunctional resin of nitrogen atom is formed byreacting NH in one oligomer with terminal Si—Cl in another oligomer asshown in the following formula, by heating. In this reaction, thetemperature of the system is preferably 40° C. to 200° C. The higher thetemperature becomes, the faster the reaction rate becomes. However, theloads of the apparatus are increased as the reaction temperature becomeshigher. Usually, an inorganic polysilazane having a weight-averagemolecular weight of 1,200 to 20,000 in terms of polystyrene is producedby the reaction at 100° C. to 200° C. for 2 hours to 10 hours.

Examples of solvent include: (A) aromatic hydrocarbons such as benzene,toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene,triethylbenzene, and decahydronaphthalene; (B) liner saturatedhydrocarbons such as n-pentane, i-pentane, n-hexane, i-hexane,n-heptane, i-heptane, n-octane, i-octane, n-nonane, i-nonane, n-decane,and i-decane; (C) cyclic saturated hydrocarbons such as cyclohexane,ethylcyclohexane, methylcyclohexane, and p-menthane; (D) cyclicunsaturated hydrocarbons such as cyclohexene and dipentene (limonene);(E) ethers such as dipropyl ether, dibutyl ether, diethyl ether, methyltertiary-butyl ether (MTBE), and anisole; and so on

In the process (b), a catalyst may be added for proceeding the reactionof Si—NH with Si—Cl. As the catalyst, tertiary amines are effective.Examples of the tertiary amines include tertiary lower-alkylamines, forexample, having 1 to 5 carbon atoms such as triethylamine,trimethylamine, diethylpropylamine, and N-ethyldiisopropylamine.Further, the tertiary amines may contain plural amino groups in amolecular and examples thereof includeN,N,N′,N′-tetramethyldiaminomethane,N,N,N′,N′-tetramethylethylenediamine, and the like. Furthermore, astertiary amines having a cyclic structure, 1-ethylpyrroridine,2,6-lutidine, 4-methylmorpholine, 1-ethylpiperidine, and the like arecited.

The amount of the catalyst is usually 0.01 to 20 times moles the amountof the oligomer, preferably 0.1 to 5 times moles, though it is varied bya catalyst used and so on. When the catalyst is used, an inorganicpolysilazane having a polystyrene conversion weight-average molecularweight of 1,200 to 20,000 is produced by reacting usually for 30 minutesto 5 hours at 60° C. to 150° C., though the reaction temperature and thereaction time are varied depend on the catalyst used.

The step (e) is a step which is conducted for removing Si—Cl in theresin produced in the aforementioned step (b). The step (c) is toterminate Si—Cl by reacting with ammonia. When Si—Cl remains in theresin, Cl will be easily dissociated in the later steps and it causesvarious failures. This step, therefore, is required. In this step,excessive NH₃ can be supplied to, for example, a reaction liquidobtained in the step (b) or a liquid in which an inorganic polysilazaneresin obtained in the step (b) is dissolved in a solvent. UnreactedSi—Cl reacts with NH₃ to form a hydrochloric acid salt. The hydrochloricacid salt is precipitated and the precipitate is removed using a filter.

The obtained inorganic polysilazane-containing solution is distilledunder a reduced pressure to obtain an inorganic polysilazane resin. Whenthe reaction liquid includes pyridine and other organic solvents asdescribed above, pyridine is usually removed by distillation and theorganic solvents are removed, as needed. When the concentration of thepolysilazane resin in the organic solvent solution is adjusted to, forexample, 5 to 30 weight % by a vacuum distillation, thepolysilazane-containing solution obtained can be used as a coatingliquid as it is or a base liquid for a coating composition. A coatingcomposition may be formed by adding other additives or solvents to thebase liquid of a coating composition if needed.

Thus, an inorganic polysilazane resin having a ratio of silicon atoms tonitrogen atoms (Si/N) of 1.30 or more, preferably 1.32 or more isobtained. In the point of view of the solubility in the organic solventand the shape of the coated film, as described above, the weight-averagemolecular weight in terms of polystyrene of the inorganic polysilazaneresin of the present invention is preferably 1.200 to 20.000.

The inorganic polysilazane resin of the present invention is dissolvedin an organic solvent and made to a solution, namely, a coatingcomposition. The coating composition is applied to a substrate. Thecoated film is dried, then subjected to an oxidation step, and, ifnecessary, annealed to form an insulation film, a planarization film, aprotective film, a passivation film, a hard mask, a stress adjustingfilm, a sacrifice film, and the like. In addition, the isolation regionmay be formed by filling the trench with the coating composition, dryingit, and then subjecting to an oxidation process.

The coating composition containing the inorganic polysilazane resin ofthe present invention will be described hereinafter. The coatingcomposition of the present invention comprises an organic solvent otherthan the aforementioned inorganic polysilazane resin. The organicsolvent may be any one which can dissolve the inorganic polysilazaneresin of the present invention and additives if used, and does not reactwith the inorganic polysilazane resin and the additives. Preferredexamples thereof include, but are not limited to, the same organicsolvents as those exemplified in the step (b) described above.

Mixture of two kinds or more of solvents are suitably used as thesolvent for controlling an evaporation rate of solvent, loweringharmfulness to the human body or adjusting solubility of componentscontained in the coating composition. Furthermore, the inorganicpolysilazane resin solution used for the coating composition may beprepared by dissolving a solid resin in an organic solvent as describedabove, or by using an inorganic polysilazane solution as it is, which isobtained without isolating the inorganic polysilazane resin at thesynthesis of the polysilazane resin, or by diluting the inorganicpolysilazane solution, or by further concentrating the inorganicpolysilazane solution by a vacuum distillation.

The coating composition containing an inorganic polysilazane resin ofthe present invention may further comprise a compound which promotes asilica conversion reaction. The compound which promotes a silicaconversion reaction means a compound promoting a reaction in whichpolysilazane is converted to a siliceous material by an interaction withpolysilazane. Various compounds has been known as the compound whichpromotes a silica conversion reaction, for example, compounds describedin JP 06-299118 A can be used as the compound. More specifically,compounds (i) to (iii) described below can be represented.

(i) Metal Carboxylates

As the metal carboxylates, metal carboxylates containing nickel,titanium, platinum, rhodium, cobalt, iron, ruthenium, osmium, palladium,iridium, or aluminum are particularly preferred. When these metalcarboxylates are used as a promoting compound, the amount thereof aremade to usually 0.01 to 20 weight-%, preferably 0.1 to 10 weight-%, morepreferably 0.5 to 5 weight-% relative to the weight of the polysilazanecompound. When the amount used exceeds 20 weight %, the composition canbe gelled and when the amount used is smaller than 0.01 weight %, theeffect of the present invention cannot be obtained. It is, therefore,necessary to be careful for the amount used.

(ii) N-Heterocyclic Compounds

As the N-heterocyclic compounds, N-heterocyclic compounds which do notshow aromaticity are preferred. Specific examples thereof include1,3-di-4-piperidylpropane, 4,4′-trimethylenebis(1-methylpiperydine),diazabicyclo-[2,2,2]octane, and cis-2,6-dimethylpiperazine. When theseN-heterocyclic compounds are used as the promoting compound, the amountused is made to usually 0.01 to 50 weight %, preferably 0.1 to 10 weight% relative to the weight of the inorganic polysilazane compound. It ispreferable that a larger amount of N-heterocyclic compound promotes aconversion to silica. However, when a larger amount of theN-heterocyclic compound is used, it should be careful as the density ofa siliceous film may decrease or the handleability of the compositionmay become worse by deterioration of stability of the polysilazane.

(iii) Amine Compounds

As the amine compounds, there are exemplified amine compoundsrepresented by the following formula (A) or (B).

In the formula (A), R^(A)s represent each independently a hydrogen atomor a C₁-C₃ hydrocarbon group and two R^(A)s attached to the samenitrogen atom are not a hydrogen atom simultaneously, L¹ and L² are eachindependently —CH₂—, —NR^(A1)— (whereas R^(A1) is a hydrogen atom or aC₁-C₄ hydrocarbon group) or —O—, p₁ and p₃ are each independently aninteger of 0 to 4, and p₂ is an integer of 1 to 4.

In the formula (B), R^(B)s represent each independently a hydrogen atomor a C₁-C₄ hydrocarbon group, and q₁ and q₂ are each independently aninteger of 1 to 4.

The blending amount of the amine compound is usually 1 to 20%,preferably 3 to 10%, more preferably 4 to 8%, further more preferably 4to 6% relative to the weight of the polysilazane compound. The blendingamount of the amine compound is preferably a given amount or more forobtaining a maximum effect of improving a promotion of the reaction anda density of a film, but on the other hand, the amount is preferably agiven amount or less for maintaining the solubility of the compositionand preventing the film unevenness detection when forming a film.

To the coating composition containing the polysilazane resin, otheradditives may be added if needed. For example, such additives are aviscosity adjusting agent, a crosslinking promoter etc. Phosphoruscompounds such as tris(trimethylsilyl)phosphate may also be contained inthe coating composition containing the polysilazane resin for agettering effect of sodium when used in a semiconductor device. Theinorganic polysilazane resin-containing solution obtained are preferablycirculating-filtered using a filter having a pore size of 0.1 μm or lessto reduce coarse particles having a particle size of 0.2 μm or more to50 particles/cc or less.

The solid content of each element described above is varied byapplication conditions, baking conditions, and so on. The solid contentof the inorganic polysilazane resin is preferably 0.1 to 40 weight %,more preferably 0.2 to 30 weight %, further more preferably 0.3 to 25weight % relative to the total weight of the coating composition. Inaddition, the contents of various kinds of additives other than theinorganic polysilazane resin are preferably 0.001 to 40 weight %, morepreferably 0.005 to 30 weight %, further more preferably 0.01 to 20weight % relative to the weight of the polysilazane compound, thoughthose are varied by the kinds of the additives etc.

Coating methods of the inorganic polysilazane resin-containingcomposition are, a spin coat method, a dip coat method, a spray coatmethod, a roll coat method, a transfer method, a slit coat method, andso on. The spin coat method is particularly preferred. The coated filmhaving the desired film thickness can be formed by one applicationaction or 2 or more of repeating application actions, if necessary.Examples of the substrate to which the coating composition is appliedincluding a silicon substrate, a glass substrate, a resin film, etc. Thecoating composition may be applied to a substrate on which asemiconductor film, a circuit, or the like was formed in a productionprocess of a semiconductor element, if necessary. The thickness of thecoated film is usually 10 to 2,000 nm, preferably 20 to 1,000 nm in adried film thickness though it is varied by the purpose of the use offilm.

After the coated film of the polysilazane resin was formed byapplication of the coating composition as described above, the coatedfilm is preferably prebaked (heat-treated) for drying. This process isperformed for complete removal of solvent contained in the coated filmand precure of the coated film in the final step of the applicationprocess. Usually, in the prebake process, the baking temperature is heldat a substantially constant temperature. However, the baking temperaturein the prebake process may be controlled as is raised with time duringthe prebake process for preventing a formation of concave in thesubstrate, which is occurred by shrinkage of the coated film, andoccurrence of voids in the trench. The temperature in the prebakeprocess is usually in the range of 50° C. to 300° C., preferably 70° C.to 200° C. The required time for the prebake process is usually 10seconds to 30 minutes, preferably 30 seconds to 5 minutes. After theprebake, a treatment liquid containing an oxidation accelerator (a cureaccelerator) may be applied to the coated polysilazane film, ifnecessary.

In the oxidation process, any treatment methods conventionally known inthe oxidation process of the polysilazane may be adopted. Thepolysilazane is oxidized by the method to form a siliceous film havingexcellent properties. The oxidation is conducted using a curing oven ora hot plate. As preferred methods, there are exemplified methods ofconducting heat treatments under an inert gas or oxygen atmosphere whichcontains water vapor, a method of conducting a heat treatment under awater vapor atmosphere containing hydrogen peroxide vapor, etc.

The concentration of water vapor in the water vapor oxidation is animportant factor for converting the polysilazane resin to a siliceousfilm (silicon dioxide) and is preferably 1% or more, more preferably 10%or more, most preferably 20% or more. Particularly, when the content ofwater vapor is 20% or more, the conversion of polysilazane resin to asiliceous film proceeds easily, defects of the film such as voids issuppressed, and properties of the siliceous film are improved. When aninert gas is used as the atmosphere gas, nitrogen gas, argon gas, heliumgas, and the like are used. The treatment temperature is varied by thecomposition of the coating liquid and, generally, the conversion rate toa siliceous film tends to become faster in a higher temperature. On theother hand, adverse influences to device properties by oxidation of asilicon substrate or change of the crystal structure tend to becomesmaller in a lower temperature. From these points of view, it isdesirable that heating is conducted at usually 900° C. or lower,preferably 200° C. to 500° C. It is desirable that the heating rate tothe target temperature is generally 0.1 to 100° C./minute and the curingtime at the target temperature is generally 1 minute to 10 hours,preferably 15 minutes to 3 hours. The treating temperature and thecomposition of the treatment atmosphere may be changed gradually, ifnecessary.

The coated film can be oxidized by exposing it to a hydrogen peroxidevapor. In this case, the coated film may be placed under a hydrogenperoxide vapor atmosphere at a temperature of 50° C. to 200° C. for oneminute to 2 hours. At this time, other vapor such as water vapor ordilution gas may be contained in the hydrogen peroxide vapor atmosphere.Generally, the higher the concentration of hydrogen peroxide is, thefaster the oxidation rate of the coated film becomes.

The inorganic polysilazane resin in the coated film is converted to asiliceous film (silicon dioxide). The converted film may be furthersubjected to an annealing treatment process in which the whole of thesubstrate is heated for completely converting and curing all of thepolysilazane-coated film to silica, if necessary. The annealingtreatment is usually conducted by putting and heating the whole of thesubstrate in a curing oven and the like, generally. The annealingtreatment may be conducted under a non-oxidizing atmosphere or anoxidizing atmosphere. The annealing temperature is usually 300° C. to1,100° C., preferably 400° C. to 1,000° C. and the treatment time isusually 10 minutes to 5 hours, preferably 30 minutes to 2 hours.

In the present invention, one or more of thin coated films may befurther formed on the coated film by repeating these processes, ifneeded. By forming two or more of coated films, the thickness of eachformed film can be reduced. As a result, when each of the coated thinfilms is cured, the sufficient diffusion and supply of oxygen from thesurface of the film can be carried out at any portion of the depthdirection of the coated thin film and a siliceous film having moreexcellent properties can be formed.

EXAMPLES

Hereinafter, the invention will be specifically described with referenceto Examples and Comparative examples. However, it should be understoodthat the present invention is not restricted by these Examples andComparative examples. In addition, weight-average molecular weights interms of polystyrene of synthesized inorganic polysilazane resins weremeasured by the following method.

<Measurement of the Weight-Average Molecular Weight>

The weight-average molecular weight was measured using a GPC apparatusmanufactured by Shimadzu Corporation with a THF eluent.

Example 1

Three moles (303 g) of dichlorosilane having a purity of 99% or morewere injected into a mixed solvent consisting of 1 kg of dehydratedpyridine and 3 kg of dibutyl ether at −30° C. under stirring. Whilemaintaining the temperature of the solution at −30° C., 2 moles (34 g)of ammonia gas having a purity of 99.9% or more were injected into themixture under stirring. The mixture was reacted for 2 hours whilemaintaining the temperature at −30° C. to obtain a solution of silazaneoligomer containing unreacted Si—Cl. The existence of the unreactedSi—Cl was confirmed by using FTIR, VIR-9450 manufactured by JASCOCorporation.

The oligomer obtained contains following compounds and the like, and thetotal number of NH and the total number of Cl in the oligomer are thesame.

In the oligomer formation process, HCl was generated but most of it wasreacted immediately with excessive pyridine to form pyridinehydrochloride and the pyridine hydrochloride formed was precipitated.The pyridine hydrochloride was removed with a glass filter.

To the reaction solution obtained, 0.5 moles (50 g) of triethylaminewere added and the reaction system was heated gradually to 120° C. andheld at 120° C. for 1 hour. Then, the solution was cooled gradually tothe room temperature to form a slurry reaction mixture. The thusobtained reaction mixture was filtered with a glass filter for removingpyridine hydrochloride to obtain a filtrate. To the filtrate obtained,dibutyl ether was added and the mixture was heated to 50° C., followedby distillation under the reduced pressure of 20 mmHg to remove pyridineat this temperature. Through these processes, Solution A having aconcentration of 20% by weight, which contains a resin (Resin A) havinga weight-average molecular weight of 5,650, was obtained.

Example 2

A silazane oligomer solution containing unreacted Si—Cl was prepared bythe same process as Example 1. To the silazane oligomer solutionobtained, 2 moles (204 g) of N,N,N′,N′-tetramethyldiaminomethane wereadded and this reaction system was heated gradually to 80° C. understirring and held at this temperature for one hour, followed by coolingdown gradually to the room temperature. Subsequently, 1 mole (17 g) ofammonia gas having a purity of 99.9% was injected again to the mixtureunder stirring and then the mixture was allowed to stand for 30 minutes.The obtained slurry reaction mixture was filtered with a glass filter toremove pyridine hydrochloride to obtain a filtrate. To the filtrateobtained, dibutyl ether was added and then heated to 50° C., followed bydistillation under the reduced pressure of 20 mmHg to remove pyridine atthis temperature. Through these processes, Solution B having aconcentration of 20% by weight, which contains a resin (Resin B) havinga weight-average molecular weight of 4,450, was obtained.

Example 3

Three moles (303 g) of dichlorosilane having a purity of 99% or morewere injected into a mixed solvent consisting of 300 g of dehydratedpyridine and 3 kg of dibutyl ether under stirring at 0° C. Whilemaintaining the temperature of the solution at 0° C., 3 moles (51 g) ofammonia gas were injected into the mixture under stirring. The mixturewas reacted for 2 hours under stirring while maintaining the temperatureat 0° C. to obtain a solution of polysilazane polymer. It was confirmedby FTIR, VIR-9450 manufactured by JASCO Corporation that the polymerdoes not contain the unreacted Si—Cl. The molecular weight of thepolymer was 2,300. Pyridine hydrochloride and ammonium chloride, whichwere formed in the synthesis process of the polysilazane polymer, wereremoved by filtration with a centrifugal separation filter.

Subsequently, 1 mole (107 g) of 2,6-lutidine was added to the filtrateand then the reaction system was heated gradually to 90° C., followed byinjecting 1 mole (101 g) of dichlorosilane at a flow rate of 0.5 L/minunder stirring. Then, the solution was cooled down to 0° C. and 1 mole(17 g) of ammonia gas having a purity of 99.9% was injected into themixture under stirring for removing the unreacted Si—Cl. The obtainedslurry reaction mixture was filtered with a glass filter to removepyridine hydrochloride and a filtrate was obtained. To the filtrate,dibutyl ether was added and then heated to 50° C., followed bydistillation under the reduced pressure of 20 mmHg to remove pyridine atthis temperature. Through these processes, Solution C having aconcentration of 20% by weigh, which contains a resin (Resin C) having aweight-average molecular weight of 7,450, was obtained.

Comparative Example 1

Three moles (303 g) of dichlorosilane having a purity of 99% or morewere injected into a mixed solvent consisting of 300 g of dehydratedpyridine and 3 kg of dibutyl ether at −30° C. under stirring. Whilemaintaining the temperature of the solution at −30° C., 2 moles (34 g)of ammonia gas having a purity of 99.9% were injected into the mixtureunder stirring. The mixture was reacted for 3 hours under stirring whilemaintaining the temperature at −30° C. The obtained slurry reactionmixture was filtered with a glass filter to remove pyridinehydrochloride and a filtrate was obtained. It was confirmed by FTIR,VIR-9450 manufactured by JASCO Corporation that the solution containedthe unreacted Si—Cl. However, when the reaction mixture was exposed tothe air, it absorbed water vapor and emitted white smoke (which ishydrochloric acid). Therefore, it was unsuitable for the precursor ofinsulator and the evaluation thereof was stopped.

Comparative Example 2

A polysilazane polymer was prepared by the same process as Example 3.That is, 3 moles (303 g) of dichlorosilane having a purity of 99% ormore were injected into a mixed solvent consisting of 300 g ofdehydrated pyridine and 3 kg of dibutyl ether under stirring at 0° C.While maintaining the temperature of the solution at 0° C., 3 moles (51g) of ammonia gas were injected to the mixture under stirring. Themixture was reacted for 2 hours under stirring while maintaining thetemperature at 0° C. The slurry reaction mixture obtained was filteredwith a glass filter to remove pyridine hydrochloride and a filtrate wasobtained. To the filtrate obtained, dibutyl ether was added and thenheated to 50° C., followed by distillation under the reduced pressure of20 mmHg to remove pyridine at this temperature. Through these processes,Solution D having a concentration of 20% by weight, which contains aresin (Resin D) having a weight-average molecular weight of 2,400, wasobtained.

<Measurement of a Ratio of Silicon Atoms to Nitrogen Atoms (Si/N)>

Each of Solutions A to D was applied to a silicon wafer and dried for 3minutes at 50° C. to remove solvent. In this process, a spin coater,1H-DX2 made by MIKASA Co., LTD and a hot plate, Charming HHP-412 made byAS ONE Corporation were used. Samples were measured by RBS (RutherfordBackscattering Spectrometry) using Pelletron 3SDH manufactured byNational Electrostatics Corp. as a measurement device. The results areshown in Table 1. From the results mentioned in Table 1, it wasconfirmed that Resins A to C were polymers in which many silicon atomswere contained.

TABLE 1 Example 1 Example 2 Example 3 Comparative example 2 Resin AResin B Resin C Resin D Si/N 1.41 1.32 1.54 1.28

<Measurement of a Shrinkage Rate and a Residual Stress of a Baked Film>

Each of Resins A to D prepared in Examples 1 to 3 and Comparativeexample 2 was spin-coated on a silicon wafer, heated to 150° C., andmaintained at this temperature for 3 minutes to evaporate the solvent.As a result, a film with 500 nm in thickness was obtained. The sampleswere baked in the steam baking furnace, VF-1000 manufactured by KayoThermo Systems Co., Ltd. for 1 hour at 350° C. under an 80% steamatmosphere. Subsequently, the steam atmosphere was changed to a nitrogenatmosphere and the samples were annealed for 1 hour at 850° C. Theshrinkage and the residual stress of each film were measured andevaluated according to the methods described below. The results areshown in Table 2.

(Shrinkage)

The shrinkage was calculated by the following formula. In the formula,“base film thickness” was defined as a film thickness after drying at150° C. for 3 minutes.

Shrinkage(%)={[(base film thickness)−(film thickness after annealtreatment)]/(base film thickness)}×100

The film thickness was measured using the reflecting spectrographic filmthickness meter made by OTSUKA ELECTRONICS CO. LTD.

(Residual Stress)

The residual stress was measured using FLX-2320 made by Tencor.

The measuring theory is as follows. When a film applied on a siliconwafer has a residual stress, the substrate (silicon wafer) will bend.The curvature radius of the substrate is measured and a stress value iscalculated from the value of the measured curvature radius.

TABLE 2 Comparative Example 1 Example 2 Example 3 example 2 Resin AResin B Resin C Resin D Shrinkage 12% 14% 10% 20% Residual stress 5 MPa10 MPa 20 MPa 20 MPa

From Table 2, it is known that problems of shrinkage and residual stressof a siliceous conversion film can be significantly improved by forminga siliceous film by use of the inorganic polysilazane resin having ahigh Si content rate of the present invention, in comparison with a casewhere a siliceous film is formed by use of the conventionally knowninorganic polysilazane having a low Si content rate, which is shown inComparative example.

1. An inorganic polysilazane resin, wherein a ratio of containingsilicon atoms to containing nitrogen atoms, Si/N is 1.30 or more.
 2. Theinorganic polysilazane resin according to claim 1, wherein a ratio ofcontaining silicon atoms to containing nitrogen atoms, Si/N is 1.32 ormore
 3. The inorganic polysilazane resin according to claim 1, whichweight-average molecular weight in terms of polystyrene is 1,200 to20,000.
 4. The inorganic polysilazane resin according to claim 1, whichis produced by heating an inorganic polysilazane compound containingboth Si—NH and Si—Cl to react NH with Cl.
 5. The inorganic polysilazaneresin according to claim 4, wherein the heating is conducted in thepresence of a catalyst.
 6. The inorganic polysilazane resin according toclaim 5, wherein the catalyst is a tertiary amine.
 7. A inorganicpolysilazane resin according to claim 1, which is produced bysynthesizing a silazane oligomer or polymer with no Si—Cl bond and thenthermally reacting the synthesized silazane oligomer or polymer with anadded halosilane.
 8. The inorganic polysilazane resin according to claim7, wherein the halosilane is a dihalosilane.
 9. A coating compositioncontaining the inorganic polysilazane resin according to claim
 1. 10. Amethod for forming a siliceous film, wherein the coating compositioncontaining the inorganic polysilazane resin according to claim 9 isapplied to a substrate and oxidized by contacting with a water vaporunder a heated condition after drying.
 11. A method for forming asiliceous film, wherein the coating composition containing the inorganicpolysilazane resin according to claim 9 is applied to a substrate andoxidized by contacting with a hydrogen peroxide vapor and a water vaporunder a heated condition after drying.
 12. A siliceous film, which isformed by the method for forming a siliceous film according to claim 10.13. The siliceous film according to claim 12, of which shrinkage is 15%or less.